The Ontario Provincial Police said a boat crashed into a small island on Six Mile Lake — north of Barrie, Ont., — at about 11:15 p.m. on Saturday.
A 70-year-old woman died as a result of the collision. Police have identified the deceased as Beverly MacDonald of Kingston, Ont.
A 46-year-old man from Athens, Ont., was taken to a Toronto hospital with serious injuries.
Four other people, including a 15-month-old boy, were taken to a local hospital with non-life threatening injuries.
Police said the boat was travelling with another vessel at the time of the crash.
The collision remains under investigation.